This application claims priority under 35 U.S.C. 119(c)(1) based on Applicants Provisional U.S. patent application Ser. No. 60/997,221 filed Oct. 2, 2007 and titled “HYDRAULIC SYSTEM VALVING”, and is a continuing application of Applicants application Ser. No. 12/154,576 filed May 23, 2008 now abandoned of same title.
1. Field
This invention is directed to improvements in hydraulic systems and particularly in the hydraulic systems of mining equipment motors which are typically constructed with a sealed case containing a power unit designed to operate under high pressure, e.g., several hundred psi, and which converts hydraulic force into mechanical motion to drive an output shaft rotatably mounted thru the case wall and thru an annular shaft seal affixed in the wall. The power unit is typically isolated from the case in semi-sealed housing structure which is designed to allow a small leakage (slippage) of hydraulic oil from the power unit thru the housing structure and into the case to thereby lubricate moving parts of the power unit such as meshing gears, pistons, wobble plates, output shaft mounting bearings, wear plates or the like. Of particular concern herein is the prevention of rapid, excessive hydraulic pressure build-up within the motor cases to an extent, e.g., 1500-2500 psi, depending on the pressure relief or by-pass valve setting in the directional control valve, which excessive pressure “blows out” the motor shaft seals and brings the mine dusting or other operation to a halt. The motor cases normally are under much lower pressures such as, for example, 20-50 psi which is also the pressure normally felt at the shaft seal.
The invention is particularly useful on dusting machines which are designed for dispersing large quantities of particulate material into the atmosphere, and particularly concerns such machines which disperse rock dust in coal mines to put down a layer of dust on the mine floor, ribs and roofs to settle coal dust and to minimize the dangers of explosion, for example, from coal dust and/or methane.
2. Prior Art
Such motors are usually bi-directionally operable and function in extremely grimy environments such as exists in underground coal mines which are not only filled with coal dust but which are daily dusted with rock dust for suppressing coal dust, gases or other dangerous materials. Such operating conditions make it practically impossible to keep the hydraulic fluid which run the motors in a clean condition and the consequent dirty, gritty hydraulic fluid results in excessive wear of the motor parts, locking up of hydraulic motors, clogging of hydraulic lines and prevention of proper closing of pressure regulating check valves or the like, all of which can contribute, to one extent or another, to an uncontrolled spontaneous rise in oil pressure within the motor case resulting in destruction of the motor shaft seal.
It is common practice to provide a motor which is used on the aforesaid mining equipment with some form of oil drain system for the motor case such that the case and shaft seal cannot be over pressurized. One form of drain system, for example, comprises the use of a case drain line which connects the case to the return line. In using a bi-directional motor, when the feed and return are reversed, a case drain valve provided by the manufacture within the motor case will reverse the drain line to the return line. However, when, as in applicants mine dusting machine described herein in detail, the motors are hydraulically connected in series from auger motor at high operating (line 144) P (e.g., 800-1000 psi), to 1st flinger motor at lower operating (line 144A) P (e.g., 500 psi), to 2nd flinger motor at still lower operating (line 144B) P (e.g., 250 psi), the bi-directional capability of the motor cannot be utilized since the flinger motors, especially their shaft seals, are not designed to operate under PTO pressure which would result from the reversal of the feed and return lines in a conventional system. Consequently, conventional case drain check valve systems cannot be used in applicants system.
Typical hydraulic motors to which the present invention is applicable include all types having a sealed output shaft such as gear (external, internal, lobe), direct drive gerotor, orbiting gerotor, roller-vane gerotor, vane balanced, and the like. Patents which show some of these types, the disclosures of which patents are hereby incorporated herein by reference in their entireties include U.S. Pat. Nos.: 6,481,990 B2; 4,981,423; 3,593,621; 2,463,950; 2,478,481; 3,619,093; 4,466,336; 4,578,020; and 4,551,080. Additionally, U.S. Patent Office Search Class 415 “Rotary Kinetic Fluid Motors Or Pumps” contain hundreds of patents further showing hydraulic motors for which the present invention is useful. Examples of such motors are given in the drawings herein and denoted “PRIOR ART”.
Further in this regard and as a primary cause of spontaneous over pressurization of the motor case and shaft seal, operation of hydraulic equipment is typically done thru operator manipulation of lever operable directional control valves (FIG. 12B) which can deliver high pressure fluid thru either a feed line or a return line, as desired, and which is mounted on the mining equipment such as a mine utility tractor. Such a control lever, for example, when pivoted forward will run a motor in one direction and when pivoted backward will run the motor in the reverse direction such as to run a hydraulically wheeled vehicle or auxiliary mining equipment thereon forwards or backwards. Typical of these vehicles are the various types of utility tractors, coal scoops, continuous miners, shuttle cars, ram cars, bolt machines and the like.
As will become apparent below, and contrary in its operation to many of the hydraulic systems of present mining machines and equipment which operators are called upon to run, an unintentional pressurization of the return line (LP) of applicants present hydraulic system by the operator for more than a few seconds in his testing of the hydraulics of applicants machine or his inadvertent manipulation of the control lever in the wrong direction would have a disastrous effect on applicants motor shaft seals.
Applicants “Mine Dusting Machine”, U.S. Pat. No. 4,673,131, the disclosure of which is incorporated herein below, describes a machine commonly used to spread limestone dust in undergound coal mines. This machine receives power from a hydraulic power take-off (PTO) that is on an underground mining machine called a scoop which carries a large amount of rock dust to be spread throughout the mine to suppress coal dust and other explosive materials. The scoop's hydraulic PTO is bi-directional, i.e., either the hydraulic feed line or the return line (hoses) may be used as high pressure (HP) or low return pressure (LP) as required since the PTO can be used with a variety of auxiliary devices and mining apparatus which require such bi-directional operation, i.e., forward and reverse operation.
Three hydraulic motors are commonly used on the “Mine Dusting Machine” and are hosed in series as shown in FIGS. 1 and 12. As further elaboration to prior systems mentioned above, bi-directional hydraulic motors are the ones readily available and by-pass or leak hydraulic oil internally into the motor case from their power units which typically comprise some form of an armature means or other hydraulically driven structure mounted within a semi-sealed housing which is in turn sealed in a motor case. The leakage goes thru the power unit and provides lubrication its to various parts and to the output shaft bearings. The leaked oil within the case is at very low pressure compared to the feed pressure. If, for example, such a hydraulic motor runs alone, the leaked oil in the case is typically ported to the hydraulic reservoir tank, which is at low pressure, by use of a drain system employing internal check valves within the case. The case drain collects the leaked oil and the internal check valves prevent excessive back pressure from developing on and disrupting, i.e., blowing out the shaft seal. However, if the motors are hydraulically connected in series as in the present system these factory installed internal check valves cannot be to prevent excessive back pressures from developing, in the motor cases since the downstream subsequent motor feed lines must be pressurized to run the downstream motors of the series.
The Mine Dusting Machine's auger motor, preferably of the Geroler® type (see FIGS. 24 and 25), is the first hydraulic motor in the series and is of such a design that its output shaft seal will withstand several hundred, e.g., 500-1,000 psi of hydraulic back pressure within the motor case without damage to the shaft seal. The second and third hydraulic motors, preferably of the meshing gear type (see FIG. 23), are used to power the flingers and are of such a design that the output shaft seals can only withstand about 60 psi without their disruption. At a higher pressure the shaft seals will be turned wrong side out—blown out—and will subsequently leak hydraulic oil, even at lower pressure as illustrated in FIGS. 13 and 14 at a sufficient rate to shut the motor down and drain the hydraulic system.
It is noted that these preferred output shaft seals, as shown in FIGS. 13, 14, 16 and 23 are termed herein as “inverted lip seals” and are constructed with one or more elastomeric annular discs having an annular shaft contact lip “L” which is pressured by an annular spring and/or the oil pressure within the motor case sealingly against the shaft. These discs can take a variety of configurations but the provision of an inverted lip is highly preferred. As the hydraulic oil becomes dirty with various types of grit and other particulate solids, the abrasiveness of the solids will wear the seal and make it easier for case pressure to disrupt the seal. Other type seals including O-ring or stuffing box types can also be blown out by excessive pressures.
These factors cause to exist the further and ever present possibility of the scoop operator pivoting the control lever in the wrong direction and throwing full hydraulic pressure, e.g., 2500 psi internally of the motor casings and thus blowing out the seals. It is noted that in the operation of hydraulic machines in general, the operator will generally test the hydraulic operation by pivoting the hydraulic levers to their forward and reverse positions by force of habit. In such a situation wherein a mine dusting machine such as applicants is being used without the protection afforded by applicants present drain system, the pressurization (HP) of the return line by mistake could be very costly.